The present invention relates to a vapor deposition apparatus for forming a semiconductor stacked layer structure, and more particularly to a vapor deposition apparatus that is suitable for forming a semiconductor heterojunction interface where there is a sharp change in composition. Also, the present invention relates to a vapor deposition process using the vapor deposition apparatus; a stacked layer structure produced by the process; a field effect transistor comprising the stacked layer structure; a semiconductor Hall device comprising the stacked layer structure; and a semiconductor light-emitting device comprising the stacked layer structure.
Conventionally, an epitaxial stacked layer structure employed in light-emitting devices of singlehetero (SH)- or doublehetero (DH)-structure or in two-dimensional electron gas field effect transistors (TEGFETs); or a structure similar to the stacked layer structure is formed by a vapor deposition technique such as metal-organic chemical vapor deposition (MOCVD) (see Solid State Electron., vol. 43 (1999), pp. 1577-1589). Particularly, when a stacked layer structure employed in a TEGFET is formed, composition must change sharply at the heterojunction interface in order to efficiently exert the effect of two-dimensional electron gas (TEG) (see Nippon Butsuri Gakkai ed., xe2x80x9cHANDOTAICHOKOSHI NO BUTSURI TO OYO,xe2x80x9d 4th printing of 1st edition, published on Sep. 30, 1986 by Baifukan, pp. 139-145).
A conventional vapor deposition apparatus in which semiconductor crystal layers, for example, group III-V compound semicoriductor crystal layers, are vapor-grown by MOCVD does not include a piping system through which a group III or group V element source passes constantly, regardless of whether or not the source is necessary for the growth of the crystal layers (see J. Crystal Growth, vol. 55 (1981), pp. 64-73, 92-106, 164-172, and 213-222). The conventional vapor deposition apparatus has a piping system so that an element source or a dopant source is supplied to a vapor deposition region through the piping only when the supply of the source is necessary. Therefore, in the apparatus, the supply of the source gas, which is temporarily unnecessary for the vapor-growth of the crystal layers, is temporarily stopped by means of valve operation.
In the piping system of such a conventional vapor deposition apparatus, when the source gas becomes necessary again, the valve must be opened to resume supply of the gas to the vapor deposition region. However, when the supply of the source gas is resumed after the supply is stopped, the flow rate of the gas varies temporarily in accordance with variance in pressure in the piping by the opening of valve. In addition, the purity of the source gas lowers, since the gas is confined or retained in the piping. Temporal variance in the flow rate of the source gas and lowering of the purity of the gas cause variance in compositional proportions of elements constituting the crystal layers. As a result, forming a junction interface where there is a sharp change in composition is difficult. Therefore, such a conventional vapor deposition apparatus having the aforementioned piping system is inappropriate for vapor-growth of a stacked layer structure, which must have a heterojunction interface where the composition changes sharply employed in a TEGFET.
In order to solve the problems involved in the piping system of such a vapor deposition apparatus and to form a semiconductor junction interface where the composition changes sharply, there has been proposed a piping system to the supply a source gas called a vent/run system, which has a mechanism that enables constant flow of a source gas and instantaneous switching of the gas supplied to a vapor deposition region (see J. Crystal Growth, vol. 68 (1984), pp. 412-421 and 466-473; and xe2x80x9cIII-V ZOKU KAGOBUTSU HANDOTAI,xe2x80x9d edited by Isamu Akasaki, published on May 20, 1994 by Baifukan, 1st edition, pp. 68-70). A vent line (exhaust line) is provided to constantly supply a source gas to the outside of a vapor deposition region in advance to maintain a constant flow rate of the gas, regardless of whether or not the gas is necessary for vapor-growth of the intended crystal layers. A run line (source supply line) is connected directly to the vapor deposition region, and is provided for supplying the source gas necessary to the region for vapor-growth of the intended crystal layers, the flow of the source gas being switched from the vent line to the run line. That is, unlike the conventional piping system containing only a source supply line, the vent/run system includes the vent line through which the source gas passes constantly.
FIG. 1 illustrates a vent/run-type source gas supply piping system. Source gas passages 13, 14, and 15 are provided for passing source gasses 10, 11, and 12, respectively. Each source gas consists of a gas source or gas accompanied by vapor of the source. The flow rates of the source gasses 10 through 12 passing through the passage 13 through 15 are regulated by flowmeters 16, 17, and 18. Conventionally, the passages 13 through 15 corresponding to the respective source gasses are connected to a run line 25 and a vent line 26 via two-way valves 19 through 24. Whether or not a fluid is passed through a single line is determined through an opening and closing operation of the corresponding two-way valve. The run line 25 is connected directly to a vapor deposition region in which crystal layers are formed. The vent line 26 is detoured away from the vapor deposition region and connected directly to an exhaust system in which exhaust of gas is carried out.
Switching of the flow of the source gasses 10 through 12 from the run line 25 to the vent line 26 and vice versa is carried out by an opening and closing operation of the flow path switching valves 19 through 24 provided on the source gas passages 13 through 15. For example, in order to switch the path through which the source gas 10 flows via the source gas passage 13 from the vent line 26 to the run line 25, the two-way valve 22 is closed and, simultaneously, the two-way valve 19 is opened. Usually, the two-way valves 19 and 22 are not opened simultaneously; nor are the two-way valves 20 and 23 and the two-way valves 21 and 24.
The conventional vent/run-type piping system consists of a combination of a single run line (i.e., the line 25) and a single vent line (i.e., the line 26). In the vent/run-type piping system consisting of such a combination; i.e., a single vent/run-type piping system, the flow rate of the source gas varies periodically immediately after the path of a source gas is switched from the vent line 26 to the run line 25. Variance in the flow rate of the source gas gradually decreases while the gas is supplied through the line 25 to a vapor deposition region, but the amount of the gas supplied to the vapor deposition region still varies. Variance in the amount of the gas supplied causes variance in the compositional proportions of elements constituting crystal layers in a vertical direction with respect to the layers, and also impedes sharp change in composition at a heterojunction interface of the crystal layers.
Problems involved in the conventional single vent/run-type source supply piping system will be described in more detail with reference to FIG. 1. For example, suppose when two source gasses 10 and 11 are passed through the run line 25 at a constant flow rate via the source gas passages 13 and 14 to thereby vapor-grow a crystal layer, and subsequently a mixed-crystal layer is vapor-grown from the three source gasses 10 through 12. In such a case, in order to grow the mixed-crystal layer, the path of the source gas 12 must be switched from the vent line 26 to the run line 25 by an opening and closing operation of the two-way valves 21 and 24. Immediately after the path is switched, the flow rate of the source gas 12 varies periodically; i.e., the flow rate becomes inconsistent. Inconsistency in the flow rate of the source gas 12 causes inconsistency in compositional proportions of elements constituting the mixed-crystal layer, the elements including the element of the source gas 12. As a result, obtaining a sharp change in composition at the heterojunction interface between the layers is difficult.
In order to vapor-grow the mixed-crystal layer from the three source gasses 10 through 12 in the conventional single vent/run-type source supplying piping system shown in FIG. 1, even when the paths of the source gasses 10 through 12 are simultaneously switched from the vent line 26 to the run line 25, the flow rate of each of the gasses varies in the line 25. This is because eliminating differences in pressure between the lines 25 and 26 is difficult. Briefly, when the flow of the source gas is switched from the vent line to the run line, the flow rate of the respective source gas varies in the run line 25. Therefore, when the source gasses, the flow rate of each having been varied, are supplied to the vapor deposition region, a mixed-crystal layer having a consistent composition cannot be grown.
The aforementioned problems are attributed to variance in the flow rate of the source gas and inconsistency in mixing proportions of the source gasses that occur during switching of the paths in the conventional single vent/run-type source supply piping system. An object of the present invention is to solve such problems.
In order to solve the aforementioned problems, the present inventor has performed extensive studies and has found that, when a piping structure in which the path of a mixture of source gasses is switched immediately after the mixing proportions of the gasses becomes consistent is provided, and the gas mixture is supplied to a vapor deposition region, a junction interface at which composition profile changes sharply can be consistently formed. The present invention has been accomplished on the basis of this finding. Accordingly, the present invention provides:
(1) a vapor deposition apparatus for producing a stacked layer structure in which semiconductor crystal layers are laminated on a substrate material, which apparatus comprises a first run line for mixing one or more vapor deposition sources with a carrier gas in advance and passing the resultant source mixture; a second run line for supplying the source mixture to a vapor deposition region; a vent line for allowing the source mixture to detour away from the vapor deposition region and discharging the source mixture; and a line switching mechanism for switching the flow of the source mixture from the first run line to either the second run line or the vent line;
(2) a vapor deposition apparatus according to (1) described above, wherein the vent line has a mechanism for passing a carrier gas;
(3) a vapor deposition apparatus according to (1) or (2) described above, wherein the first run line has two or more of flow path switching mechanisms for switching the flow of source mixture to either the second run line or the vent line;
(4) a vapor deposition apparatus according to any one of (1) through (3) described above, wherein the apparatus comprises an apparatus for measuring differences in pressure between the vent line and the first or second run line;
(5) a vapor deposition apparatus according to any one of (1) through (4) described above, wherein the vapor deposition sources contain a hydride of group V or VI element;
(6) a process for the vapor deposition of a stacked layer structure by use of a vapor deposition apparatus as recited in any one of (1) through (5) described above, which process comprises switching the flow of the vapor deposition sources that have been mixed in the first run line in advance from the vent line to the second run line after the mixing proportions of the sources have become consistent;
(7) a process for vapor-growth of a stacked layer structure by use of a vapor deposition apparatus as recited in any one of (1) through (5) described above, which process comprises switching the flow of the vapor deposition sources that have been mixed in the first run line in advance from the vent line to. the second run line when a difference in pressure between the first and second run lines is 5xc3x97102 Pa or less;
(8) a vapor deposition process according to (6) or (7) described above, wherein a stacked layer structure is produced through metal-organic chemical vapor deposition;
(9) a stacked layer structure produced through a vapor deposition process as recited in any one of (6) through (8) described above;
(10) a stacked layer structure according to (9) described above, which is a multi-stacked layer structure having a heterojunction structure;
(11) a stacked layer structure according to (10) described above, which is a multi-stacked layer structure for producing a field effect transistor;
(12) a stacked layer structure according to (11) described above, wherein the multi-stacked layer structure for producing a field effect transistor has a heterojunction between gallium indium phosphide (GaXIn1xe2x88x92XP: 0xe2x89xa6Xxe2x89xa61) and gallium indium arsenide (GaYIn1xe2x88x92YAs: 0xe2x89xa6Yxe2x89xa61);
(13) a stacked layer structure according to (11) described above, wherein the multi-stacked layer structure for producing a field effect transistor has a heterojunction between aluminum indium arsenide (AlXIn1xe2x88x92XAs: 0 less than Xxe2x89xa61) and gallium indium arsenide (GaYIn1xe2x88x92YAs: 0xe2x89xa6Yxe2x89xa61);
(14) a stacked layer structure according to (10) described above, which is a multi-layer structure for producing a group III-V compound semiconductor Hall device;
(15) a stacked layer structure according to (14) described above, which is a multi-layer structure having a heterojunction between indium phosphide (InP) and gallium indium arsenide (GaYIn1xe2x88x92YAs: 0xe2x89xa6Yxe2x89xa61);
(16) a stacked layer structure according to (10) described above, which is a multi-layer structure for producing a group III nitride semiconductor light-emitting device;
(17) a stacked layer structure according to (16) described above, which is a multi-layer structure having a heterojunction between aluminum gallium nitride (AlXGa1xe2x88x92XN: 0xe2x89xa6Xxe2x89xa61) and aluminum gallium indium nitride ((AlXGa1xe2x88x92X)YIn1xe2x88x92YN: 0xe2x89xa6Xxe2x89xa61, 0xe2x89xa6Y less than 1);
(18) a field effect transistor comprising a stacked layer structure as recited in (11) described above;
(19) a field effect transistor according to (18) described above, which comprises a stacked layer structure containing an active layer formed from gallium indium arsenide (GaYIn1xe2x88x92YAs);
(20) a group III-V compound semiconductor Hall device comprising a stacked layer structure as recited in (14) described above;
(21) a group III-V compound semiconductor Hall device according to (20) described above, which comprises a stacked layer structure as recited in (15) described above;
(22) a group III nitride semiconductor light-emitting device comprising a stacked layer structure as recited in (16) described above; and
(23) a group III nitride semiconductor light-emitting device according to (22) described above, which comprises a stacked layer structure as recited in (17) described above.